The present invention concerns a filtering unit comprising a filter diaphragm, a backing surface placed against the diaphragm, a passage through which the liquid to be filtered can be supplied on one side of the diaphragm, and a channel by which the filtered liquid can be removed from the opposite side of the diaphragm, and said backing surface presenting ridges giving support to the filter and grooves therebetween, through which in connection with filtering the liquid can move parallel to the diaphragm.
Manual filtering practiced on a laboratory scale is usually accomplished with filtering funnels or other equivalent vessels, the filter papers or diaphragms used in them being discardable, that is, single-use. On the side of said vessels such filtering units are used in which the filter diaphragm has been placed between two opposed horizontal backing members and in which the liquid to be filtered can be introduced on one side of the diaphragm and the liquid drained through the diaphragm can be removed from the opposite side of the diaphragm. The said backing members are in most instances nets or gratings having the purpose to afford as uniform support as possible to the filtering diaphragm without in any way impeding the draining of the liquid through the diaphragm.
In a filtering unit known in prior art, the filtering diaphragm has been disposed to rest on a backing surface placed against the diaphragm and in which a spiralling groove has been provided which starts at the centre of the surface and leads to its periphery. In this filtering unit, the liquid to be filtered that has been introduced at the centre of the backing surface will spread along the spiralling groove over the entire area of the diaphragm, while at the same time liquid is drained through the diaphragm to the opposite side thereof. But this design has the drawback that the flow resistance of the long, narrow spiralling groove is high, for which reason the whole filtering unit is unsatisfactory as to its filtering capacity.
The filtering units of prior art mentioned above have the feature in common that discardable, single-use filter diaphragms are used in them. Since the diaphragms are quite low in price, this has not been considered a significant detriment, but it should still be noted that changing the diaphragm after each filtering run constitutes an extra, time-consuming work step. Moreover, in recent time the need has become apparent to develop apparatus which would automatically perform the filtering, and in such types of apparatus provision for changing the filtering diaphragm would quite obviously result in unreasonably complicated designs. There exists therefore a need to provide a filtering unit in which the filtering diaphragm is cleanable between filtering runs and which thereby would be particularly suitable for use as a component in automatically operating filtering apparatus.